Fucosyltransferase 3 (FUT3), also known as blood group Lewis alpha -4-fucosyltransferase (Lewis FT), CD174, LE, Les, FT3B, FucT-III or galactoside 3(4)-L-fucosyltransferase, is a type II membrane protein that belongs to the fucosyltransferase family. This protein is 361 amino acid (aa) in length and it consists of a 15-aa cytoplasmic tail, a 19-aa transmembrane region and a 327-aa ectodomain. It is reported that 99% of the human FUT3 amino acid sequence is identical to that of chimpanzee.

The protein encoded by FUT3 gene is an enzyme with both alpha (1,3)-fucosyltransferase and alpha(1,4)-fucosyltransferase activities, catalyzing the addition of fucose to precursor polysaccharides in the last step of Lewis antigen biosynthesis. Researches have shown that Fucosyltransferase 3 may catalyze alpha-1,3 and alpha-1,4 glycosidic linkages involved in the expression of Vim-2, Lewis A, Lewis B, sialyl Lewis X and Lewis X/SSEA-1 antigens. In addition, this protein may play a role in blood group Lewis determination and mutations in FUT3 gene are responsible for the majority of Lewis antigen-negative phenotypes.